Juvenile Dermatomyositis, the most common of the pediatric inflammatory myopathies, is a systemic pediatric autoimmune disease. There is no experimental model for JDM, greatly limiting our understanding of the pathophysiology of the disease process, which, like other autoimmune diseases, is associated with premature cardiovascular compromise and chronic inflammation. Heritable genetic factors, either unique or shared with other autoimmune diseases, predispose the child to develop JDM in concert with environmental influences, such as UVB exposure, season of birth and antecedent infection. Characterization of muscle-specific molecular pathways is severely constrained by the limited amount of involved muscle from the diagnostic biopsy available for research studies. We have documented dysregulation at the mRNA level and aberrant miRNA control in the muscle of untreated children with JDM, as well as active production of cytokines by the muscle fibers themselves, suggesting that they participate in the immune response, and are not only targets of it. A recent discovery showed that mononuclear cells, present in a small amount (5ml) of peripheral blood, can be reprogrammed by infecting them with a non-integrating Sendai virus to create induced pluripotent stem cells (iPSC). IPSCs share many traits with embryonic stem cells; they can induce the formation of teratomas when transplanted into mice, and give rise to a wide spectrum of differentiated cell types-among them myogenic progenitor cells, which then develop into muscle. In this study we will derive a single cell population of myogenic precursor cells from iPSCs from 3 sets of monozygotic twins discordant for JDM and their matched healthy controls in order to characterize the genetic contribution of muscle to disease pathophysiology. We hypothesize that the differentiated muscle cells derived from iPSCs will recapitulate molecular differences, associated with phenotype that we have previously identified in the transcriptome (miRNAs and mRNAs) of muscle biopsies from untreated children with JDM vs healthy controls. In Specific Aim #1, we will derive and compare iPSCs from three sets of monozygotic twins: one diagnosed with JDM, one unaffected-- and an age, gender, race matched control in order to: a) Verify their pluripotency by teratoma formation in a murine host and, b) Induce the embryoid body cells to form skeletal muscle in vitro. The unaffected twin will serve as a specific genetic and environmental control. Specific Aim # 2 will characterize the transcriptome differences, using RNAseq and miRNA assays, between: 1) the iPSCs from JDM, unaffected twin and healthy matched control as well as 2) their iPSC-derived myogenic cells to determine differences in IPSc and muscle from each donor as well as between donors. The Bioinformatics analysis will normalize the data and identify differentially expressed genes and their pathways in both the iPSCs and their derived muscle cells for each donor. The success of this project will lead to greater understanding of inflammatory myopathy and will open up a new avenue for pathophysiological investigation of JDM and other autoimmune diseases.